Mounting evidence suggests a history of traumatic brain injury (TBI) can increase the risk of developing Alzheimer's disease (AD). A pathological clue linking these two disease states came with the observation that amyloid-beta (A2) plaques, a hallmark pathology of AD, could be found in patients within hours following TBI. Furthermore, excessive plaques can be observed, persisting even decades after the initiating trauma. More recently, we have identified that the A2- degrading enzyme, neprilysin, may play an important role in the emergence of plaques. It has also been demonstrated that just a single TBI can induce the delayed emergence of neurofibrillary tangles (the other hallmark pathology of AD) and stands as important evidence in the link between these two disease states. While AD-like pathologies after TBI have been studied primarily in younger adults, little is known about how the aged brain responds to trauma with regard to these pathologies. Using a unique human brain archive based in Glasgow, UK, we propose to examine post-mortem brain tissue of elderly individuals for AD-like pathologies following TBI. Specifically, we aim to 1. Examine for the hallmark pathologies of Alzheimer's disease (A2 plaques and NFTs) in individuals aged 60+ who have sustained a TBI. 2. Examine of A2 degrading enzyme, neprilysin, in individuals aged 60+ who have sustained a TBI, using immunohistochemistry and 3. Examine of the influence of polymorphisms of both the neprilysin gene Apolipoprotein E (ApoE) gene in predicting amyloid-2 plaque formation in individuals aged 60+ who have sustained a TBI. As AD is predominantly a disease of ageing, we hypothesize that older individuals will be have increased vulnerability to developing AD-like pathology post-TBI. Exploration of these mechanisms may provide an important basis for improving the clinical management and developing therapeutic opportunities for this unique subgroup of individuals. ) PUBLIC HEALTH RELEVANCE: Traumatic brain injury (TBI) is a risk factor for Alzheimer's disease (AD). Both Hallmark pathologies of AD - A2 plaques and neurofibrillary tangles, have been found following TBI. Preliminary data suggests older individuals may be an increased risk of these TBI-induced pathologies. Using a unique human brain archive, we propose to examine older individuals for AD-like pathologies following TBI. Potential findings may explain the worsened neurocognitive outcomes observed following TBI in older patients. Understanding the mechanistic basis of these processes is vital in the drive towards targeted therapeutic intervention - particularly as novel AD-therapies emerge into the clinical forum. )